Tears Of Protesilaos?

I add that it doesn't look like a broken die, at least to me..

This is to the point that I seriousley wonder whether this couldn't be intentional. A drop of sweat?

I remember you the story : at the arrival of the Greeks on the beach of Troy, none of the soldiers is courageous enough to jump from the boats, because an oracle told that the first greek soldier who would land on the ground of Troy would be killed. Even the great Achilles doesn't move. Protesilaos is the one who jumps from the boat and he is killed soon after by Hector.

I never noticed that before, but would agree that it has to be intentional. As you suggest a drop of sweat or possibly a tear. A mystery we will probably never know.